This varnish has been employed by cabinet makers upon their ware, but not generally as a finishing varnish. It has generally been employed when much diluted for the purpose of filling the pores of the wood to form a good body, previous to the application of copal or finishing polish. Shellac is prepared from a gummy substance deposited upon trees by an insect. Seed-lac is more costly ind better than shellac, being the select part? Irom the trees, free from many impurities, which exist in the latter, either kind forms a varnish when dissolved in alcohol, which alcohol should be a good article: say 0'80 to )'85, spe. gr. This is the kind of varnish most frequently used by pattern makers, & c, but is tiardly suitable for furniture or other sim.'iu." irticles, on account of its containing a yellowish coloring matter, which injures the appearances of the surface to which it is applied. Cabinet makers therefore employ a bleached solution of shellac particularly for white r light colored woods. The bleaching of shellac is generally effected on a large scale by chlorine or some of its compounds, or by ulphuric acid; the bleached article costs ibout 50 cents per lb., and the unbleached less than half this sum. The bleached shellac is frequently dissolved in spirits of wine for use is a varnish by cabinet makers. This varnish is quite apt to stain any inlaid metallic jrnament upon the furniture, or any metal attached to it, in consequence of the varnish retaining a small portion of the bleaching compound in solution. Another process of bleaching may be adopted, which renders the varnish free from this objection, and very much reduces the cost ot the bleached article of shellac or seed-lack. This process consists in the use of animal charcoal as a bleaching powder. It is prepared in the following manner. Any quantity of yellow shellac, previously broken in small pieces is conveyed into a flask, alcohol of 0'83 sp. gr. poured upon it and the whole heated on the hob, or, in the summer in the sum, until the shellac is dissolved ; upon this, so much coarsely powered inimal charcoal is added to the solution that the whole forms a thin paste, the flask is closed, not quite air-tight, and left so for sometime, exposed to the sun ; and in eight to fourteen days a small sample is filtered sufficient to ascertain whether it has acquired a light yellowish brown color, and whether it yields ? clear, pure polish on light-colored woods. If this be the case it is filtered through coarse blotting paper, for which purpose it is best to employ a tin-funnel, with double sides similar to those employed in filtering spirituous solutions of soaps in the preparation of transparent soaps opedeldoc, & c. The portion which first passes through the filter may be preserved separately, and be used as a ground or first polish. Then some more spirit is poured over the charcoal upon the filter, and the solution used as a last coating. The solution ot shellac purified by animal charcoal has a brown yellow color, but it is perfectly clear and transparent, when diluted with alcohol, the color is so slight that it may be used in this state for polishing perfectly, white wood, such as maple, pine, & c, without the wood acquiring the least tint of yellow. Shellac can be dissolved by an alkali, but it is rather a saponaceous compound, and it does not make a good varnish for resisting water. It is best to dissolve it in alcohol in order to get a good varnish, and one that will combine with coloring matters for various purposes. By adding some lampblack to alcholic lac varnish, a beautiful varnish for black leather is produced.
This article was originally published with the title "Shellac Varnish for Furniture, &C"